Skeletal and Integumentary Systems: Study Guide

Skeletal System

Structure and Function of Bone

The skeletal system provides structural support, protection, and facilitates movement. Bones are dynamic organs composed of various tissues and cells.

• Compact Bone: The dense, outer layer of bone that provides strength and structure. The structural unit is the osteon (Haversian system).

• Spongy Bone: The porous, inner part of bone that contains red bone marrow.

• Osteocytes: Mature bone cells responsible for maintaining bone tissue.

• Osteoblasts: Cells that build new bone matrix.

• Osteoclasts: Cells that break down bone matrix.

• Lacunae: Small spaces housing osteocytes.

• Canaliculi: Tiny channels connecting lacunae, allowing for nutrient and waste exchange.

• Periosteum: A dense membrane covering the outer surface of bones, containing nerves and blood vessels.

• Endosteum: A thin membrane lining the medullary cavity of bones.

Example: The femur's shaft is composed mainly of compact bone, while its ends contain spongy bone.

Bone Development and Growth

Bones develop through two main processes: intramembranous and endochondral ossification.

• Intramembranous Ossification: Bone develops directly from mesenchymal tissue (e.g., flat bones of the skull).

• Endochondral Ossification: Bone develops by replacing hyaline cartilage (e.g., long bones like the femur).

• Epiphyseal Plate: Growth plate where new bone is produced during childhood and adolescence.

Example: The humerus grows in length at the epiphyseal plate until adulthood.

Types of Bones and Bone Classification

Bones are classified by shape and structure.

• Long Bones: Longer than they are wide (e.g., femur, humerus).

• Short Bones: Cube-shaped (e.g., carpals, tarsals).

• Flat Bones: Thin and broad (e.g., skull, ribs).

• Irregular Bones: Complex shapes (e.g., vertebrae).

• Sesamoid Bones: Embedded within tendons (e.g., patella).

Bone Remodeling and Homeostasis

Bone is constantly remodeled through the actions of osteoblasts and osteoclasts, regulated by hormones and mechanical stress.

• Calcium Homeostasis: Maintained by parathyroid hormone (PTH) and calcitonin.

• Vitamin D: Essential for calcium absorption and bone health.

• Wolff's Law: Bone adapts to the loads under which it is placed.

Equation:

$\text{Bone Mass} = \text{Bone Formation} - \text{Bone Resorption}$

Types of Fractures

Fractures are breaks in bone, classified by their characteristics.

• Simple (Closed) Fracture: Bone breaks but does not pierce the skin.

• Compound (Open) Fracture: Bone breaks and pierces the skin.

• Comminuted Fracture: Bone shatters into several pieces.

• Greenstick Fracture: Incomplete break, common in children.

• Transverse, Oblique, Spiral: Classified by the direction of the break.

Diseases and Disorders of Bone

• Osteoporosis: Decreased bone density, increasing fracture risk.

• Osteomalacia/Rickets: Softening of bones due to vitamin D deficiency.

• Osteogenesis Imperfecta: Genetic disorder causing brittle bones.

Bone Marrow

• Red Marrow: Site of hematopoiesis (blood cell formation).

• Yellow Marrow: Stores fat; found in the medullary cavity of long bones.

Connective Tissues

Types and Functions

Connective tissue supports, binds, and protects other tissues and organs.

• Bone: Rigid connective tissue providing structure.

• Cartilage: Flexible tissue at joints, ear, nose.

• Blood: Fluid tissue transporting nutrients and waste.

• Adipose Tissue: Stores fat for energy and insulation.

• Dense Connective Tissue: Forms tendons and ligaments.

Example: Hyaline cartilage covers the ends of long bones at joints.

Integumentary System

Structure and Function of Skin

The skin is the largest organ, providing protection, sensation, and regulation of body temperature.

• Epidermis: Outermost layer, composed of stratified squamous epithelium.

• Dermis: Middle layer, containing connective tissue, blood vessels, nerves, and appendages.

• Hypodermis (Subcutaneous Layer): Deepest layer, mainly adipose tissue.

Layers of the Epidermis

The epidermis consists of several layers (from deep to superficial):

• Stratum Basale: Deepest layer, site of cell division.

• Stratum Spinosum

• Stratum Granulosum

• Stratum Lucidum: Present only in thick skin (palms, soles).

• Stratum Corneum: Outermost, dead keratinized cells.

Skin Appendages

• Hair: Provides protection and sensation.

• Nails: Protect the tips of fingers and toes.

• Glands: Sebaceous (oil), sweat (eccrine and apocrine), and ceruminous (earwax) glands.

Functions of the Skin

• Protection against pathogens and injury

• Regulation of body temperature

• Sensation (touch, pain, temperature)

• Excretion of waste products

• Vitamin D synthesis

Skin Color

• Melanin: Pigment produced by melanocytes; determines skin color.

• Carotene: Yellow-orange pigment from diet.

• Hemoglobin: Red pigment in blood, visible in fair skin.

Wound Healing and Regeneration

• Skin can regenerate after injury through cell division in the stratum basale.

• Scar tissue forms when damage is extensive.

Types of Membranes

• Mucous Membranes: Line body cavities open to the exterior (e.g., respiratory, digestive tracts).

• Serous Membranes: Line closed body cavities; secrete serous fluid.

• Cutaneous Membrane: The skin.

• Synovial Membranes: Line joint cavities; secrete synovial fluid.

Cartilage

Types and Locations

• Hyaline Cartilage: Most common; found at joints, nose, trachea.

• Elastic Cartilage: Flexible; found in ear, epiglottis.

• Fibrocartilage: Strongest; found in intervertebral discs, pubic symphysis.

Summary Table: Bone and Skin Comparison

Feature	Bone	Skin
Main Function	Support, protection, movement	Protection, sensation, regulation
Main Cell Types	Osteocytes, osteoblasts, osteoclasts	Keratinocytes, melanocytes, fibroblasts
Layers	Compact, spongy, periosteum, endosteum	Epidermis, dermis, hypodermis
Vascularity	Highly vascular	Variable; epidermis avascular, dermis vascular
Regeneration	Limited (depends on damage)	High (especially epidermis)

Additional info:

• Some details, such as the specific names of bone diseases and the process of bone healing, were expanded for academic completeness.

• Table content was inferred and organized for clarity.